Electric timepiece of transistor type



FIG. 2

y 7, 1968 TOMOHACHI TSUKAGOSHI ETAL 3,381,467

ELECTRIC TIME IPIECE OF TRANSISTOR TYPE Filed Jan. 5, 1966 2 Sheets-Sheet 1 FIG.

IHIHIIIIIII I] l I I I Attomey May 7, 1968 TOMOHACHI TSUKA'GOSHI ETAL 3,331,467

ELECTRIC TIMEPIECE OF TRANSISTOR TYPE 2 Sheets-Sheet Filed Jan. 5. 1966 //V VEN TORS Tomohachi Tsukagoshi Ken j/ To/ri/a United States Patent 0 8 Claims. c1. ss--2s ABSTRACT OF THE DISCLOSURE Electric timepiece with a transistorized energizing circuit for a drive motor having a permanent-magnet rotor interposed as a coupling between a pair of eelctromagnetic coils connected, respectively, in the input and output circuits of the transistor, the rotor shaft being coupled to an output shaft, and to a speed-regulating mechanism 0 including an escapement wheel, via a pair of aligned shafts interconnected by a spiral leaf spring. The transmission between the rotor and the speed-regulating mechanism may include a pair of'imeshing gears transmitting torque in one direction only while blocking rotation in 25 the opposite direction.

This applicaton is a continuation-in-part of our prior application Ser. No. 387,088 filed on Aug. 3, 1964, and now abandoned.

This invention relates to an electrically operated timepiece w'hose time-keeping mechanism is driven by a transistor motor supplied with power from a low voltage power source such as a battery.

While an ideal battery-operated timepiece is one where- 'in accurate rate is constantly maintained irrespective of variations in the voltage of the power supply, a study of timepieces of this type known heretofore reveals that this basic aspect has apparently been grossly neglected. That is, the conventional practice has favored the application of driving power directly to the rate-governing mechanism comprising a balance or tuning fork, which functions as a time-standard oscillation member, as the simplest and easiest arrangement. For this reason, a drop in the supply voltage causes a variation in the driving power, a deviation in the amplitude of the governing mechanism, thereby a disturbance of the rate, and, therefore, an undesirable impairment of the performance of the entire mechanism as a time-keeping device.

In order to provide a governing mechanism operating with an amplitude which is unvarying even with respect to voltage drop, the following three conditions must be satisfied:

(l) A motive power source capable of driving fully over a prolonged period of time is provided.

(2) The construction of the speed-regulating mechanism does not impede free oscillation.

(3) The driving power is constant at all times and, moreover, is capable of easily producing the optimum output.

The present invention is based on a full consideration of the foregoing conditions.

It is an object of the present invention to provide a timepiece whose time-keeping mechanism is driven by an electric motor capable of producing a constant output at all times irrespective of variations in the supply voltage.

Another object of the present invention is to provide, in

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the time-keeping mechanism driven by the above-mentioned motor, a magnetic coupling means of unique con struction of members having low residual magnetism thereby to couple a driving shaft and a driven shaft with a constant, small torque.

Still another object of the invention is to provide a shaft to which an escape wheel coupled to a speed-regulating mechanism is fixed, said shaft being coaxially aligned with the driving shaft to tnansmit a low constant torque, without direction conversion or speed reduction of driving power, directly to the escapement wheel.

Yet another object of the invention is to facilitate the adjustment of the supplied torque through the aforementioned unique construction of the magnetic coupling means.

A further object of the invention is to provide an arrangement wlhereby driving power is transmitted to the regulating mechanism via the magnetic coupling means, a leaf spring and the like so as not to impede the free oscillation of the speed-regulating mechanism.

A still further object of the invention is to provide an electric timepiece of high accuracy yet low cost which can 'be easily installed and contained within a small confined space.

The nature, principle, and details of the invention, as well as the features and advantages thereof, will he more clearly apparent from the following detailed description given with respect to a preferred embodiment of the invention when read in conjunction with the accompanying drawing in which like parts are designated by like reference numerals and characters, and in which:

FIG. 1 is a side view, mostly in section and with parts cut away, showing the essential parts of the electrical timepiece embodying the invention;

FIG. 2 is a schematic diagram showing the circuit of a motor used for providing motive power in the timepiece shown in FIG. 1;

FIG. 3 is a planar view taken in the direction and plane indicated by arrow III in FIG. 1 and showing the essential parts of a magnetic coupling device according to the invention;

FIG. 4 is a planar view taken in the direction and plane indicated by the arrow IV in FIG. 1 and showing a leaf-spring device for transmitting driving power;

FIG. 5 is a side-sectional view showing another example of the magnetic coupling device according to the invention;

FIG. 6 is a planar view, with parts cut away, taken in the direction and plane indicated by arrow VI in FIG. 1 and shovw'ng the regulating mechanism and gears for transmitting movement to the indicator shaft;

FIG. 7 is an enlarged, fragmentary, planar view taken in the direction and plane indicated by arrow VII in FIG. 1 and showing the meshed gear teeth of two gears;

FIG. 8 is a planar view taken in the direction and plane indicated by arrow VIII in FIG. 1 and showing a motor starting mechanism; and

FIG. 9 is a side-sectional view showing still another example of the magnetic coupling device according to the invention.

Referring to FIG. 1, the mechanism shown therein is supplied with motive power by a motor driven by an electrical circuit to be described hereinafter and having a generating coil 10 and a drive coil 9 wound on spools 2 which are mounted with a definite spacing therebetween on a frame plate 1, flanges 2,, of the spools being secured to the frame plate 1 by means such as screws 4. A rotor 8 consisting of a permanent magnet and fixed to a rotating shaft 5 is interposed between projections 3 of the spools 2, the drive coil 9 and generating coil 10 being wound on the projections 3 and having terminals a, b and c, d, respectively, which are connected as shown in FIG. 2.

One terminal b of the drive coil 9 is connected to the collector of a transistor 11 of PNP junction type. One terminal c of the generating coil is connected through a capacitor 12 to the base of the transistor. The other terminals a and d of the coils 9 and 10 are directly connected to each other and, furthermore, are connected through a battery power source 13 to the emitter of the transistor 11 and through a bias resistance 14 to the base of the transistor. The permanent magnet of the rotor '8 is fixed to the shaft 5 via a non-magnetic sleeve 6 interposed therebetween so as to prevent magnetization of the shaft 5. The shaft 5 is supported to rotate freely with little friction at its pivot ends 5,, and 5 turning in bearings 7 of a type ordinarily used in timepieces. The rotation of the motor shaft 5 is transmitted through a pinion 15 fixed thereto to a gear 18 which is meshed with the pinion 15, transmission of power through the engagement of the pinion 15 and the gear 18 being possible in only one rotational direction becauses of the unsymmetrical shapes of their gear teeth as shown in FIG. 7. Thus, the gear 15 will entrain the gear 18 in the direction indicated by the arrows, when the curved surfaces of their respective teeth interengage. If, however, the sense of rotation is reversed, the shoulder 50 of one of the teeth of gear 15 will come to rest against the point 51 of a confronting tooth of gear 18 so that rotation is blocked.

The gear 18 is so supported as to be freely rotatable coaxially about a driving shaft 19, which is rotatably supported by the frame plate 1 and a bearing plate 17 supported rigidly by a pillar 16 rigidly fixed to the frame plate 1. A cylindrical magnet 20 with four poles is fixed integrally and coaxially to one side of the gear '18. A holding plate or yoke 21 with perpendicularly bent ends 21 and with a shape which is symmetrical about the centerline of the shaft 19 is fixed to the shaft 19, the ends 21,, being parallel to the shaft 19 and to the cylindrical surface 20 of the magnet 20. Armature elements 22 made of pure soft iron are bonded onto and supported by the inner surfaces of the ends 21,, in a manner to face the cylindrical surface 20,, in close proximity thereto on opposite sides of the magnet 20. Thus, magnetic coupling is eflfected between the gear 18 and the shaft '19.

To the free extremity of the shaft 19, there is fixed an arm 26 for rigidly holding the outer end 27,, of a spirally wound blade 27, which exerts a spring force upon an escape wheel 31 to impart escapement speed thereto and whose other inner end 27,, is rigidly fixed, as shown in FIG. 4, to a holding collar 28 fixed to one end of a driven shaft 29. The shaft 29 is separated from the driving shaft 19 but is aligned coaxially therewith, being rotatably supported by a bearing plate which is rigidly supported by the pillar 16.

The escape wheel 31 is fixed to the driven shaft 29 and operates in cooperation with an anchor 32 whose motion is caused to be synchronized with that of a speed-regulating mechanism 33 timed by an oscillator such as a balance, similarly :as in an ordinary clock, whereby a control mechanism is established. A pinion is also fixed to the driven shaft 29 and is meshed with a gear 35 fixed to an indicator shaft 36.

The aforementioned motor is started by a motor-starting device which is suported on a support plate 38 rigidly fixed to a pillar '37, which in turn is rigidly mounted on the frame plate 1. The motor-starting devices comprises essentially a guide sleeve 40 fixedly fitted at one end in a hole 39 in the support plate 38 and having a bore which serves as a bearing surface, a starting. shaft 42 having at one end a control knob 41 and rotatably fitted in said bore of the sleeve 40, a starting lever 43 fixed to the other end of the starting shaft 42 and having at one end an elastic tongue-like member 46, a stop stud 44 fixed at one end to the plate 38 and serving as a stop for the other end of the lever 43, and a coil spring 45 loosely fitted about the sleeve 40 and fixed at one end to the starting lever 43 and at the other end to the stop stud 44. The member 46 of the starting lever 43 is normally held away from the pinion 15 of the motor shaft 5 as indicated in FIG. 8.

In order to prevent reverse rotation of the driving shaft 19, it is also provided with gears 23 and 24 having a relationship similar to that of the pinion 15 and the gear 18 whereby rotation is transmitted in only one direction as shown in FIG. 7. Gear 24 is journaled on a nondriven stud shaft 53.

The timepiece of the above-described construction and arrangement according to the invention operates in the following manner. When the rotor 8 of the motor is at rest, no voltage whatsoever is induced in the generating coil 10, which is furthermore cut off from the motor circuit by the capacitor 12. However, since a voltage is applied by the bias resistance 14 to the transistor 11, a D-C current is always flowing through the drive coil 9, which is functioning as an electro-magnet with its N pole constantly maintained toward the side of the rotor 8. Accordingly, the motor is at rest in an angular state where an S pole of the rotor 8 is being attracted and directed toward the drive-coil N pole. The current flowing through the drive coil at this time when the rotor 8 is at rest is approximately three times the ccrrent at the time of normal operation of the motor.

To start the motor, the knob 41 is manually turned against the force of the coil spring 45 thereby to cause the elastic tongue-like member 46 at one end of the starting lever 43 to impart a starting movement to the pinion 15 of the motor shaft 5, whereupon an alternating voltage is generated in the generating coil 10 and applied to the base of the transistor 11.

Consequently, on the transistor side, the induced voltage of the generating coil 10 causes a pulsating current to be supplied to the drive coil 9. The coils and the transistor 11 are so connected that the pulsating current at this time is applied in the reverse direction with respect to the D-C current caused to flow constantly through the drive coil 9 by the battery 13. Since the constantly flowing D-C current is selected to be of a value which is considerably higher than that of the current during the normal operation of the motor, the magnetic pole of the drive coil 9 is still excited as an N pole. Consequently, when the N pole of the rotor 8 passes by this N pole of the drive coil 9, the rotor 8 is simultaneously subjected to a repulsion force, and, as the next N pole passes by the generating coil 10, the above-described operation is repeated, whereby the motor is continuously driven.

Thus, the energy for driving the rotor 8 is determined bythe magnitude of the current on the collector side flowing through the drive coil 9, and this magnitude of the collector-side current is determined (in inverse proportion) by the current supplied to the base side by the generating coil 10.

Furthermore, since the magnitude of the current flowing to the base side is determined by the rotational speed of the rotor 8, if this rotational speed of the rotor 8 varies, the driving power will accordingly vary. When a load is applied to the rotor 8, and the rotational speed thereof is thereby decreased, the driving current increases, whereby the driving power is increased, and the original rotational speed is rapidly restored. Thus, speed control with respect to load is afforded.

The rotation of the pinion 15 of the motor shaft 5 is transmitted to the gear 18 with which the pinion 15 is meshed, whereupon the magnet 20 secured integrally to the side of the gear 18 rotates in magnetically coupled relationship with the small soft-iron pieces 22 provided on the inner surface of the holding plate 21 fixed to the driving shaft 19, the soft-iron pieces 22 being disposed with a small gap in the radial direction between said pieces 22 and the magnet 20, whereby the rotation is transmitted to the driving shaft 19.

The small gap between the magnet and the soft-iron pieces 22 is important for positively transmitting the amount of rotation produced by the motor to the driving shaft 19, and adjustment of this gap can be accomplished readily and simply by moving either outwardly or inwardly the bent ends 21,, of the holding plate 21.

The rotation of the driving shaft 19 is transmitted through the spiral leaf spring 27 fixed at its outer end 27 to the arm 26 secured to the end of the shaft 19, and adapted to impart escape speed to the escape wheel 31 via the holding collar 28 fixed to the driven shaft 29. The escape wheel 31 thereupon transmits rotation to the gear 35 fixed to the indicator shaft 36 as it performs the proper escapement in cooperation with the anchor 32 and speedregulating mechanism 33. It will be noted that the two coaxial shafts 19, 29 are journaled in separate bearings constituted by support plates 1, 17 and 25, 34, respectively.

The above-described rotational operation is thus continued. Since the relationship in terms of rotational ratio between the motor rotational speed and the escape speed of the escape wheel is set on the basis of the case wherein the motor speed is reduced to its minimum caused by occurrences such as a voltage drop, the operation proceeds with excess speed when high voltage is being supplied. Accordingly, an unvarying torque representing an optimum for the speed-regulating mechanism is constantly supplied to the thin plate 27.

During the above-described operation, reverse rotation of the driving shaft 19 is prevented by the gears 23 and 24 which are so formed as to allow only forward rotation as mentioned hereinbefore.

In order to further indicate the novelty and utility of the present invention, the following comparison of its essential features with those of a prior disclosure as per U.S. Patent 2,988,868 is considered as pertinent.

First, the two inventions differ in the operational features of their motors. In the motor of the prior disclosure when the magnet constituting the rotor is inactive, almost no current flows in the circuit, and when the rotor rotates at high speed, a large current flows. Consequently when a load is applied on the motor, the rotational speed of the rotor drops by an amount corresponding to the magnitude of the load, and as a result the driving torque decreases. For this reason, a substantially long time is re-,

quired for the rotational speed to be restored to its original value. In an extreme case, when the load is high, the rotation of the motor stops.

In contrast, in the motor according to our invention, a current is caused to flow at all times in the motor circuit as described hereinbefore. Accordingly, when the rotational speed drops because of the application of a load to the motor, the current flowing through the drive coil is increased to increase the driving torque, and when the motor rotates at a high speed, this current flowing through the drive coil is decreased, whereby the consumed current is reduced.

Secondly, the two systems differ in their transmission of driving power by means of magnetic coupling. According to the prior disclosure, a first magnet rigid with a driving shaft driven by the motor and a second magnet fixed to another shaft disposed coaxially relatively to the driving shaft with a bearing plate interposed therebetween are provided. The two ends of the second magnet are so bent that their end surfaces confront the ends of the first magnet at a predetermined distance therefrom, and by the resulting magnetic coupling the rotation of the driving shaft is transmitted to the other shaft.

Adjustment of the spacing between these two magnets is accomplished by adjustably shifting the second magnet with bent ends, but since this magnetic coupling is in the axial direction, the adjustable magnet tends to shift after a prolonged period of operation because of the attractive force of the magnets, loosening of the set screw,

and other reasons, and play in the thrust direction develops in the shaft. A further disadvantage is that in the adjustment of the magnet spacing, a screw must be retightened at each instance of adjustment.

In contrast, according to our invention the magnetic coupling is accomplished in the radial direction between a cylindrical magnet fixed to a gear which is freely rotatable about the driving shaft and small soft-iron pieces secured to the inner surfaces of bent parts of a holding plate fixed to the driving shaft, said bent parts extending alongside the cylindrical side surface of the magnet on opposite sides thereof. Accordingly, there is almost no wear of the shaft due to prolonged operation, and, moreover, adjustment of the gap between the magnet and the soft-iron pieces can be easily and simply accomplished by merely deflecting the above-mentioned bent parts outwardly or inwardly.

Furthermore, according to the prior system a bearing plate is interposed between the magnet on the drivingshaft side and the magnet on the driven-shaft side. For this reason, eddy currents are generated between the two magnets and the bearing plate. Consequently, when a coupling slip occurs, the rotational speedof the driving shaft varies, and, moreover, the motor power consumption increases, whereby a constant torque cannot be transmitted to the driven shaft.

In contrast, according to our invention the magnetic coupling does not produce any eddy currents because of the arrangement, as described hereinbefore, wherein the rectangular small soft-iron pieces integrally secured to the holding plate which is fixed to the driving shaft are disposed to confront in the radial direction the magnet which is integrally secured to the gear 18 driven by the motor. Accordingly, there is no occurrence of variation of eddycurrent magnitude due to variation in the rotational speed of the driving shaft, and a constant torque can be transmitted continually to the driven shaft. Moreover, the motor power consumption at the time of a slip in the magnetic coupling is low.

In a modification of the magnetic coupling mechanism as shown in FIG. 5, the outer end 27,, of the leaf spring 27 is fixed to a projection 21 rigid with the holding plate 21 which is fixed to the driving shaft 19, and the inner end 27,, of the spring 27 is fixed to a collar 28' secured to the driven shaft 29. By this construction, the magnetic coupling mechanism can be further miniaturized into a compact form.

A still more compact mechanism can be readily attained by another modification as illustrated in FIG. 9, wherein the aforedescribed gear 18 freely rotatable about the driving shaft 19 in the embodiment shown in FIG. 1, is replaced by a permanent magnet 47 which is used in place of the rotor 8 of the motor, and the drive coil 9 and the generating coil 10 of a motor circuit of the composition and arrangement shown in FIG. 2 are provided on the peripheral sides of the magnet 47 thereby to form a motor. Magnets 20 and 47 are mounted on a common sleeve 52 freely rotatable about shaft 19.

Considering again the aforementioned comparison, the third point of difference resides in the manner of transmitting to the escape wheel the rotation transmitted through the magnetic coupling. According to the prior disclosure, the rotation is changed by a worm and worm wheel into a rotation about an axis perpendicular to the driven shaft, and a spur gear is fixed to the shaft of the worm wheel, the outer end of an intermediate driving spring of spiral form being fixed to the worm-wheel and the inner end being fixed to the worm Wheel shaft.

The rotation of the spur gear is transmitted to a gear for controlling the fourth wheel, and said gear actuates a control device consisting of the escape wheel, anchor,

and speed-regulating mechanism. The driving spring stores surplus winding force, causes automatic slipping action, and limits the power transmitted by the magnetic coupling or slip means.

In contrast, according to our invention the speed-reduction shaft and the escape-wheel shaft coaxially aligned therewith are coupled by a leaf spring for affording escape speed, the rotation of the driving shaft being transmitted directly to the escape wheel, and rotation is transmitted to the indicator shaft as escapement-speed regulation is accomplished by a control device consisting of said escape wheel, anchor, and speed-regulating mechanism.

Accordingly, in the timepiece of the present invention, a mechanism for changing shaft direction and space therefor are unnecessary, and, moreover, rotation is transmitted directly to the escape-wheel shaft. Therefore, it is possible to eliminate completely variations in transmitted torque arising from fabrication, assembly, and design. Furthermore, since the coupling means between the driving shaft and the driven shaft is a simple leaf spring for imparting escape speed, there is no necessity whatsoever for supervision of the spring.

As described above, the present invention provides a timepiece wherein a gear disposed in a freely rotatable manner about a driving shaft is rotated by a motor capable of driving over a long period of time, and, through the utilization of a magnetic coupling mechanism comprising a magnet rigid with said gear and small soft-iron pieces fixed to the driving shaft in positions to confront the magnet, the motor rotation is transmitted directly to the escape wheel of a time-keeping mechanism in a manner such that no impediment whatsoever is imparted to the isochronous movement of the balancing staff.

Thus, by the construction and arrangement of parts according to the invention, driving power is transmitted by way of a magnetic coupling and a leaf spring to the speed-regulating mechanism of the time-keeping device whereby isochronous oscillation in the regulating mechanism is accomplished as the amplitude thereof is maintained constant at all times, and an accurate rate can be sustained.

Another advantageous feature of the invention is that, since a current is flowing at all times through the drive coil of the motor, almost no variation in the motor output is caused by variation in the power-source voltage and by application of a load to the motor shaft.

A further feature of the invention is that, since the gears in the drive mechanism have teeth forms designed to transmit rotation in only one sense reverse rotation of the motor is prevented.

Furthermore, since the magnetic coupling is effected in the radial direction of the magnet, that is, in the direction perpendicular to the magnet axis, there is no vibration and almost no shaft wear due to causes such as shifting of the magnet, and, moreover, adjustment of the gap in the magnetic coupling mechanism can be simply and easily accomplished. Accordingly, adjustment of the rate can be carried out in a positive and accurate manner.

A still further feature of the invention is that, since the magnetic coupling mechanism and the escape wheel of the time keeping mechanism are disposed in coaxial alignment with the driving shaft, mechanisms such as a speed-reduction gear train and a motive power conversion device are entirely unnecessary. Accordingly, the time-piece according to be present invention is adaptable to miniaturization, simplification of construction, and quantity (mass) production and, moreover, has the advantages of being relatively free of trouble, of long service life, and of low manufacturing cost.

It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen, for purposes of disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What we claim is:

1. In an electric timepiece having a motor, an energizing circuit for driving said motor at a substantially constant speed, an output shaft, transmission means connecting said output shaft with said motor, and speedregulating means including an escapement wheel positively coupled with said output shaft, the improvement wherein said transmission means comprises a driving shaft coupled with said motor, a driven shaft coaxial with said driving shaft, means forming separate bearings for said driving and driven shafts, said escapement wheel being carried on said driven shaft, and a leaf spring linking said driving shaft with said driven shaft for joint rotation, said leaf spring being spirally curved about the common axis of said driving and driven shafts.

2. The improvement defined in claim 1 wherein said driving shaft is provided with a generally radial projection, said leaf spring having an end relatively remote from said axis secured to said projection and an end relatively close to said axis secured to said driven shaft.

3. The improvement defined in claim 2 wherein said transmission means further includes a permanent magnet with radially directed poles centered on said axis, said magnet being positively coupled with said motor for rotation thereby, armature elements positioned to confront said poles with slight radial spacing therefrom, and a yoke rigid with said driving shaft supporting said armature element, said projecting forming part of said yoke.

4. The improvement defined in claim 3 wherein said motor comprises a magnetic rotor body centered on said axis adjacent said magnet and directly connected therewith.

5. In an electric timepiece having a motor, an energizing circuit for driving said motor at a substantially constant speed, an output shaft, transmission means con necting said output shaft with said motor, and speedregulating means including an escapement Wheel positively coupled with said output shaft, the improvement wherein said transmission means comprises a driving shaft coupled with said motor, a driven shaft coaxial with said driving shaft, said escapement Wheel being carried on said driven shaft, and a leaf spring linking said driving shaft with said driven shaft for joint rotation, said leaf spring being spirally curved about the common axis of said driving and driven shafts, said transmission means including a pair of meshing gears provided with unsymmetrical teeth for unidirectional torque transmission and blocking of reverse rotation, one of said gears being rigid with said driving shaft.

6. The improvement defined in claim 5 wherein said motor has a rotor shaft rigid with the other of said gears.

7. The improvement defined in claim 5 wherein the other of said gears in provided with a nondriven stud sha t.

8. In an electric timepiece having a motor, an energizing circuit for driving said motor at a substantially constant speed, an output shaft, transmission means connecting said output shaft with said motor, and speedregulating means including an escapement wheel positively coupled with said output shaft, the improvement wherein said transmission means comprises a driving shaft coupled with said motor, a driven shaft coaxial with said driving shaft, said escapement wheel being carried on said driven shaft, and a leaf spring linking said driving shaft with said driven shaft for joint rotation, said leaf spring being spirally curved about the common axis of said driving and driven shafts, said energizing circuit including a pair of electromagnetic coils, a transistor having an input circuit in series with one of said coils and an output circuit in series with the other of said coils, and a source of direct current in said output circuit, said motor including a permanently magnetic rotor disposed adjacent said coils for electromagnetic coupling therewith, said input circuit including a biasing connection to said source for maintaining said transistor in a highly conductive state in the absence of pulses induced in said one of said coils by rotation of said rotor whereby the current flow in said output circuit during standstill 9 10 of said rotor is substantially greater than the average 1,962,659 6/1934 Kautz 310103 current flow during rotation thereof. 2,988,868 6/ 1961 Lavet et a1. 5823 References Cited FOREIGN PATENTS UNITED STATES PATENTS 5 2,665 4/ 1907 Great Britain. 452,652 5/1891 Stahlberg 58-121 292,725 6/1916 Germany- 2,970,427 2/1961 Douglass 58-117 3 134 220 5 /1964 Meisner RD B. WILKINSON, Primary Examiner.

107,273 9/1870 Mathiuet 58-139 M. LORCH, L. FRANKLIN, Assistant Examiners. 

